1. Field of the Invention
The invention relates to the field of electronic timing devices, and more particularly, to a tide prediction apparatus and method in a compact, portable and/or hand-held tide predicting watch.
2. Background Information
Navigators, fishermen, yachtsmen and shore dwellers everywhere have a need for accurate information concerning the prediction of tides Small craft and cabin cruisers using inland waters need to know the tide and the time it will occur so that they may safely travel without the hazards of low water making navigation treacherous.
By around 1650, it was generally accepted that the movements of the tides were connected with the Moon. Lunar tides are the effect of the Moon's gravitational pull acting on water on the surface of the Earth. The Sun's gravity also has an effect, but less than half that of the Moon's. The magnitude and time lag of the response of the water on the Earth to the pull of the Sun, Moon and other tide generating forces, varies according to terrestrial conditions, such as the depth, shape and size of the sea in a particular tidal area. Spring tides occur when the Sun and Moon are in conjunction (New Moon) or opposition (Full Moon). With these tides, the height and range of the tides is greater than at other times. Neap tides occur when the Sun and Moon are in quadrature, acting at right angles to each other. Neap tides have higher low water and lower high water than average with a range that is smaller than at other times. Perigee and Apogee tides occur because the Moons orbit is elliptical so that its distance from the Earth varies during the month. At Perigee the Moon is closest and at Apogee farthest from the Earth. Meterological and geographic conditions cause differences between the tides predicted on the basis of the forces described above and actual tides. Winds and barometric pressure changes, due to storms for instance, cause variations in the height of the tides. River estuaries and narrow tide channels also affect tidal profiles. Because of the multitude of effects, it is important to have the most accurate and up to date tidal predictions science can provide.
Around 1830, the first tide predictions for the United States were published in The American Almanac. In 1883, William Ferrel introduced the Maxima and Minima Tide Predictor. This machine summed nineteen constituents, e.g., a harmonic element of the tide generating force derived from the relative positions of the Earth, Moon and Sun. This machine predicted high and low tides from 1885 to 1914.
In 1912, Rollin A. Harris and E. G. Fischer produced an analog machine that summed 37 constituents. The National Oceanic and Atmospheric Administration (NOAA) used this machine, known as "Old Brass Brains" from 1912 through 1965. Presently NOAA displays it in its headquarters in Washington, D.C.
In 1965, analog to digital tide gauges were introduced. In 1966, electronic digital computers began to compute all constituents as described in the Manual of Harmonic Analysis and Prediction of Tides, U.S. Coast and Geodetic Survey.
The output of NOAA's computers, plus local secondary offset observations and constants, creates their published Tide Table predictions, which appear daily in almost all newspapers published within 150 miles of the Atlantic, Pacific and Gulf of Mexico coast lines, and in numerous almanacs and smaller publications of local interest. Both the radio and TV media broadcast tide times throughout the day. The end users of this information are coastal pilots, small and large power or sail boaters, fishermen, both recreational and commercial, coastal residents, marine engineers, skin and scuba divers, beachcombers, and others with an interest in marine or nautical oriented activities. The tide tables produced by NOAA give good accuracy, but are inconvenient to use. Usually, one has to look up the primary Reference Station, correct for Daylight Savings Time, look in the back for published offsets, and then determine the predicted tide at a station near your location
Computer programs exist for home use on home computers to predict tides using average times between tides, and there are some portable tide predicting devices available. These existing systems have various drawbacks and limitations.
Banner, U.S. Pat. No. 3,982,104 discloses a time and tide calculating device for wrist watches, clocks and calculators that registers the tides and the time of the tides, comprising rotatable concentric tide and calender discs placed adjacent to a clock face for indicative registration and cooperation with time telling devices. These mechanical discs are rotated and tide data indicated by markings on the discs. This device relies on an average tide occurrence lag of 50 minutes each day, which makes it inaccurate since the "time lag" varies each day, sometimes being greater and sometimes less than the average. This average is based on the idea that tides follow the Moon slavishly, and ignores other effects In fact, the interval which the Moon takes to appear to circle the Earth increases and decreases as the lunar month progresses. Also, changing locations requires resetting the device or renders it useless. For instance, at Galveston, Tex., tide tables reveal that usually there are two high and low tides per day, but that sometimes only one high and one low tide occur per day. The intervals from day to day vary from a few minutes to nearly two hours. Hence, tide predictions using this device have substantial limitations.
Showalter, U.S. Pat. No. 4,412,749 discloses a programmable electronic time and tide clock which displays the real time, whether the next tide will be a high or low tide, and the time the next high or low tide will occur. This device's operation is based on an average time plus a single interval correction between peak high and low tides, with its inherent inaccuracies as mentioned earlier. Changing locations would make the device go completely out of synchronization.
There is known a digital LCD watch with a programmed tide indicator which operates to indicate tide height and rise/fall. It is programmed to indicate future tide conditions for up to 364 days in advance. It has five modes of operation including an alarm mode, a countdown timer mode, a tide set mode in which tide table data is entered into the device manually for day one of a particular month and location, a future tide mode in which, after entering data in the tide set mode described above, one enters a future month day and time to have the tide state and conditions for that future time displayed, and a time set mode for conventional time and calendar setting. The device utilizes a six hour twelve minute cycle which is an average high to low tide interval, and thus is generally inaccurate as mentioned earlier. When a location is changed, this average cycle device becomes completely out of synchronization.
There is also known a tide prediction device which comes in East Coast and West Coast versions. The East Coast version operates through the year 1999 and includes 3076 tide locations and 1416 current locations. The West Coast version operates through the year 2003 and includes 1147 tide locations and 902 current locations Software updates are required to extend the operating life of the device as well as add new tide and current locations when released by NOAA. The device is hand-held and battery operated. It will compute the next high, low, minus, or ebb tide, the next flood or slack current, the height and direction of the tide at any time, and the speed and direction of the current at any time. There is no provision for providing custom ports, i.e., for calculating the tide occurrences at locations offset from the 3076 included in the East Coast version, for instance.
Thus there has been a need for a tide prediction apparatus which is both highly accurate, reflecting true tide values as opposed to average values, and flexible, providing for custom offset locations, to overcome these and other drawbacks present in the existing systems.